Internal combustion engines are sized to power loads expected in specific applications. In cases where expected loads can vary widely an engine must be sized to power the maximum load required by the application. For example, an engine in a vehicle should deliver sufficient power to achieve a desired acceleration when the vehicle is fully loaded. A problem in many applications is that the average power output required of an engine can be much lower than the maximum power output required by the application. This can result in lower than optimal fuel efficiency.
U.S. Pat. No. 6,318,310 B1, granted Nov. 20, 2001 to Clarke, discloses a dual mode internal combustion engine which may operate in either a power mode or an efficient mode. The engine has two four-cycle combustion chambers and a two-cycle compression/expansion chamber. The valve system is set up to introduce a fluid charge into the compression/expansion cylinder during the power mode. The fluid charge is compressed in the compression/expansion chamber and one of the combustion chambers. During the efficiency mode, the fluid charge is expanded first in one of the combustion chambers and further expanded in the compression/expansion chamber.
U.S. Pat. No. 7,080,622 B1, issued Jul. 25, 2006 to Belloso, discloses a multi-cylinder internal combustion engine for a vehicle which is divided into at least two power producing sub-units designated primary and secondary sub-units. The primary sub-unit operates during all powered movement of the vehicle. The secondary sub-unit is activated only when additional power is needed. When inactive, no fuel is delivered to the secondary sub-unit, and there is no movement of its components. Each sub-unit has its own crankshaft. The crankshafts are connected by a clutch mechanism interactive with a single output shaft that delivers power to wheels of the vehicle.
U.S. Pat. No. 7,032,385 B2, issued Apr. 25, 2006 to Gray, Jr., discloses an internal combustion engine for a vehicle which provides variable displacement by selectively driving one or more engine crankshafts mounted within an engine block. In several embodiments, the crankshafts are connected to a common output shaft with a one-way clutch between the common output shaft and at least one of the crankshafts. In one aspect, starter gearing is independently associated with each of the first and second crankshafts and a starter is provided for selective engagement with the starter gearing of either of the crankshafts. In another aspect, an accessory drive for driving accessory systems of the vehicle receives power from any crankshaft which is operating, yet is isolated from any crankshaft that is not operating by a one-way clutch.
There remains a need for improved efficiency internal combustion engine systems for vehicles and other applications.